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| 55 | <H1><A NAME="SECTION0021300000000000000000"> |
| 56 | 19.3 Python Abstract Syntax</A> |
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| 58 | |
| 59 | <P> |
| 60 | The <tt class="module">compiler.ast</tt> module defines an abstract syntax for |
| 61 | Python. In the abstract syntax tree, each node represents a syntactic |
| 62 | construct. The root of the tree is <tt class="class">Module</tt> object. |
| 63 | |
| 64 | <P> |
| 65 | The abstract syntax offers a higher level interface to parsed Python |
| 66 | source code. The <a class="ulink" href="http://www.python.org/doc/current/lib/module-parser.html" |
| 67 | ><tt class="module">parser</tt></a> |
| 68 | module and the compiler written in C for the Python interpreter use a |
| 69 | concrete syntax tree. The concrete syntax is tied closely to the |
| 70 | grammar description used for the Python parser. Instead of a single |
| 71 | node for a construct, there are often several levels of nested nodes |
| 72 | that are introduced by Python's precedence rules. |
| 73 | |
| 74 | <P> |
| 75 | The abstract syntax tree is created by the |
| 76 | <tt class="module">compiler.transformer</tt> module. The transformer relies on the |
| 77 | builtin Python parser to generate a concrete syntax tree. It |
| 78 | generates an abstract syntax tree from the concrete tree. |
| 79 | |
| 80 | <P> |
| 81 | The <tt class="module">transformer</tt> module was created by Greg |
| 82 | Stein<a id='l2h-5025' xml:id='l2h-5025'></a> and Bill Tutt<a id='l2h-5026' xml:id='l2h-5026'></a> for an |
| 83 | experimental Python-to-C compiler. The current version contains a |
| 84 | number of modifications and improvements, but the basic form of the |
| 85 | abstract syntax and of the transformer are due to Stein and Tutt. |
| 86 | |
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